Self-routing multi-stage photonic interconnect

ABSTRACT

An apparatus and method for transferring data messages between a sending station and a receiving station through a photonic multi-stage interconnect network (MIN). The MIN has a plurality of switches in each stage and has a plurality of inputs and outputs. Each output of each switch is connected to one of the inputs on each switch in the next succeeding stage of the interconnect device. The sending station or terminal selects a plurality of routing messages, one routing signal for each stage of the MIN, and also sends a data message or signal to a selected receiving terminal. Each routing message is sacrificial and thus ends at the stage of the MIN where it actually operates on a switch. After all routing messages are sent, one for each stage of the MIN, a path exists to the receiving station and the data message or signal is transferred.

CROSS REFERENCE TO CO-PENDING APPLICATIONS

U.S. patent Ser. No. 07/958,148, filed Oct. 7, 1992, for EXTENDEDDISTANCE FIBER OPTIC INTERFACE in the name of N. Patel and, U.S. patentSer. No. 07/912,972, filed Jul. 10, 1992, for FIBER OPTIC BUS AND TAGADAPTER FOR BLOCK MULTIPLEXER CHANNEL in the name of N. Patel areassigned to the assignee of the present invention and are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to transfers of data betweendata origination stations and data reception stations through a networksuch as a multi-stage interconnect network and more particularly relatesto transfers of data which may utilize a fiber optic transmissionmedium.

2. Description of the Prior Art

It has been known for some time to transfer digital data messagesbetween a data origination or sending station and any one of a pluralityof message receiving terminals through a message routing device. Thoseof skill in the art will be familiar with a number of systems which useelectrical modes of data transfer. U.S. Pat. Nos. 4,975,906 and5,144,622, issued to Takiyasu et al. discuss a local area network (LAN)approach. Somewhat more recently, optical media have been employed forthe transmission of digital information.

U.S. Pat. No. 3,710,348, issued to Craft, discusses the design and useof standardized interconnect modules. Each of the modules providescircuitry for the conversion of signals to and from externaltransmission lines and to and from internal logic levels. The modulesutilize internal storage arrays for buffering of data and providecircuitry for handling control signals which are transmitted separatelyfrom the data signals. Additional circuits are used to provide paritygeneration and checking features.

The major problems associated with the Craft technique result inrelatively slow communication between the sender and receiver eventhough the standardized interface may yield some system leveladvantages. U.S. Pat. No. 5,168,572, issued to Perkins, gives thepromise of greater speed by employing a technique suitable for use withoptical media. The buffering feature is eliminated with the generalpurpose switching elements providing optical paths for multiple levelsof switching. However, separate paths are required for control of theswitching elements. Similarly, U.S. Pat. No. 4,731,878, issued to Vaidyateaches the need for separate electrical control circuitry to routeoptical data streams.

An alternative approach is shown in U.S. Pat. No. 5,175,777, issued toBoettle. With this technique, the data signals are transmitted overshared pathways using wavelength division multiplexing. However,separate signal paths are required for control signals with theimplication that these paths are electrical in nature, which is similarto the Vaidya approach. The control and data information are packed intothe same packets in the electrical system of U.S. Pat. No. 4,771,419,issued to Graves et al. Unfortunately, by packing the control and datainformation together, the entire message must be buffered within each ofthe switch elements to permit the switch element to unpack the routinginformation. This introduces significant delays into the transmissionprocess and necessitates substantially more hardware to implement. U.S.Pat. No. 4,701,913, issued to Nelson, similarly requires buffering ofthe message.

SUMMARY OF THE INVENTION

The present invention overcomes disadvantages found in the prior art byproviding an improved optical multi-stage self-routing interconnectapparatus and method which provides for the use of a system of datatransfer apparatus which can select a data path between a sending andreceiving station through its transfer network without the use ofseparate paths for control signals or buffering of the data.

A key feature of the present invention is the transfer of the switchingcontrol signals over the same information paths as the data signals.Significant amounts of hardware are eliminated in this fashion, becauseeach connection thus requires only a single interface for both datatransmission and control. This advantage is particularly beneficial whenconsidering that the prevalent means for transferring control signals inthe prior art employs the electrical medium even though the data may betransmitted optically. When used in non-blocking, multi-stageinterconnect network (MIN), as in the preferred mode, this automaticallyensures coincidence of control and data signal paths.

To implement the preferred mode of the present invention, switchingcontrol signals for routing are packed as sacrificial routing messages.These routing messages are utilized by the initial, intermediate, andterminal switch elements for routing of the associated data signals,with one routing message being dedicated to each stage within therouting path. The routing messages are sacrificial in that each isabsorbed by the switching element at the corresponding stage withoutproviding it to the next succeeding stage or the system user. The resultappears transparent. Even though there is a slight amount oftransmission path band pass consumed through transmission of thesacrificial routing packets, system band pass is not reduced, becausethe time required to activate the switch at each stage is overlapped bythe transmission of the corresponding routing message.

Because of this overlap, the data message on the single data path is ineffect delayed by an amount of time needed to complete the switchingfunction at each stage. As a result, no buffering of the data is neededat any of the intermediate stages of the switching network. In this waythe switching process occurs in real time at each stage. Sacrificing ofthe routing message at each stage effectively shortens the totaltransmission time to each of the succeeding stages.

As implemented in the preferred mode, the individual crossbar switchingelements are active in nature. Therefore, the number of stages withinthe switch is not limited by transmission losses. However, eachadditional stage does add a corresponding propagation delay.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of the present invention and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, in which like reference numerals designate like partsthroughout the figures thereof and wherein:

FIG. 1 is a block diagram showing the basic apparatus of this invention;

FIG. 2 is a block diagram showing a multi-stage interconnect network(MIN) for use in this invention;

FIG. 3 is a diagram of an individual switch element of the type to beused in the MIN of FIG. 2;

FIG. 4 is a diagram of a message sending station;

FIG. 5 is a diagram of a message receiving station;

FIG. 6 is a block diagram of a three stage MIN illustrating theoperation of the method and apparatus of this invention;

FIG. 7 is a schematic diagram showing the relationship betweensacrificial routing messages and the corresponding data message; and,

FIG. 8 is a schematic diagram showing the relationship of the messagesof FIG. 7 as routed through the MIN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of the apparatus of this invention showing aphotonic multi-stage interconnect network (MIN) 10. Min 10 is connectedto receive input signals for both routing and information messages fromany one of a plurality of sending stations or terminals such asterminals 20, 21 and 23. A first sending station is shown at 20, asecond station is shown at 21, and an nth station is shown at 23. MIN 10is also connected to provide output signals for information messages toa plurality of receiving stations or terminals 30, 31 and 33. A firstreceiving station is shown at 30, a second station is shown at 31, andan nth receiving station is shown at 33.

As will be more fully described below, the routing signals received byMIN 10 from any one of stations 20, 21 and 23 are sacrificial controlsignal packets. These control signal packets are utilized by MIN 10 toroute the associated data signals within MIN 10 and are then destroyed(i.e. not propagated beyond MIN 10). Thus the only signals presented byMIN 10 to a selected one of stations 30, 31 and 33 are informationmessage signals.

FIG. 2 shows MIN 10 in block diagram form. Min 10 includes a pluralityof switching stages, wherein each stage contains a plurality of switchelements. A first stage 40 includes a first switch element 41, a secondelement 42 and an nth element 43. A second stage 50 of MIN 10 includes afirst element 51, a second element 52 and an nth element 53. A thirdstage 60 of MIN 10 includes a first element 61, a second element 62 andan nth element 63.

Each of switch elements 41-43, 51-53 and 61-63 has a plurality of inputand output connections, more specifically described below and shown inFIG. 3. For example, in FIG. 2, line 44 depicts a connection between anoutput of one of the plurality of sending stations such as station 20 inFIG. 1 and one of the plurality of inputs of element 41 of stage 40.Line 45 depicts the connection of one of the plurality of outputs ofelement 41 routed to, for example, input line 56 connected to one of theplurality of inputs on element 52 of stage 50. Line 57 depicts theconnection of one of the plurality of outputs on element 52 to, forexample, input line 68 connected to one of the plurality of inputs onelement 63 of stage 60. Finally, line 69 depicts a connection betweenone of the plurality of outputs on switch 63 and one of the receivingstations such as station 33 (see also FIG. 1).

The pattern for routing information messages through MIN 10 broadlydescribed above is repeated in specific detail below and is morecompletely shown in FIG. 6.

FIG. 3 shows a block diagram of a switch element such as element 41 ofFIG. 2. Element 41 includes a four-by-four crossbar switch 70.Preferably switch 70 is a 4×4 Active Photonic Crossbar Switch availablefrom McDonnell Douglas Electronic Systems Company --Lasers andElectronic Systems, MC 111--1221, Box 516, St. Louis, Mo. 63134--0516.However, similar devices are available from Photonic IntegratedResearch, Inc., Allied Signal, Inc., and other similar suppliers.

Switch 70 has a plurality of inputs 71, 72, 73 and 74. Element 70 alsohas a plurality of outputs 75, 76, 77 and 78. Input 71 is connected to adecoder 81. Input 72 is connected to a decoder 82. Input 73 is connectedto a decoder 83. Input 74 is connected to a decoder 84. Each of decoders81-84 is connected to the input of a switch controller 85, whichcontroller 85 is connected to crossbar switch 70. Decoders 81-84 covertthe control signals of the sacrificial packets into electrical signalsfor use by switch controller 85.

When an operator of one of sending stations 20, 21 or 23 decides on arouting path, the routing signals appear on one of inputs 71-74 ofswitch 70, and thus at the corresponding one of decoders 81-84. Thedecoded output signal is presented to controller 85 as an electricalsignal, which responds to the decode algorithm by controlling switch 70and selecting the desired one or more outputs 75-78. The operator of thesending station will have also sent information message signals to theselected of inputs 71-74, signals will pass through to the selectedoutput(s) 75-78 to be directed to the corresponding input of one or morereceiving stations 30, 31 or 33. The routing messages may involve thesimple addition of a one of four address to the normal messageinitiation and termination codes associated with the particular protocolin use as suggested by the above cited prior art documents incorporatedherein by reference.

FIG. 4 shows a block diagram of the internal structure of sendingstation 20. Station 20 includes a User's input station 65 which can beany one of several devices, such as a computer, with which the User canenter his information message and select a receiving station such asstation 33. The User's input is sent by station 65 to a networkinterface unit 80 which comprises a route control device 86, a messagequeue device 87 and a message buffer 88.

If a path to the selected receiving station has already beenestablished, the message from station 65 passes straight through messagebuffer 88 and MIN 10 to the selected receiving station. If the desiredpath does not currently exist, or if a path is established to anunselected receiving station, then the data message from station 65 isentered into the message queue device 87 and route control device 86 isactivated to provide a path to the selected receiving station. Therouting algorithm to be used is determined by switch controller 85. Suchrouting algorithms are readily known in the art for routing signalsthrough non-blocking, multi-stage switching networks. The type ofrouting algorithm used is determined by the network applicationrequirements. Control device 86 generates a number of sacrificialrouting messages equal to the number of switching stages. FIG. 2 shows athree stage MIN and therefore three sacrificial routing messages wouldbe used to establish a path from a sending station to a receivingstation. These sacrificial routing messages are packed into asacrificial routing packet immediately preceding the desired message.This combined message is then passed through output line 25 to acorresponding input of MIN 10. The passage of these messages through MIN10 is described in:detail in the discussion of FIG. 6, below.

FIG. 5 shows a typical receiving station 30 which includes a User'sreadout station 90, such as a computer, a message queue device 91, and amessage buffer 92. When a message has completed a path through MIN 10,it will be sent on output line 35 to station 30. Note that only the datamessage arrives at line 35 because the apparatus of this invention usessacrificial routing signals, as is more fully described in thediscussion of FIG. 6, below. Yet only the data portion of the message isactually received by receiving station 30. The message on line 35 willbe placed into buffer 92 where it can be read directly to User's station90, or can be read to message queue device 91 for later viewing by theUser.

FIG. 6 shows a three stage example of multi-stage interconnect network(MIN) 10. MIN 10 in this example has three stages with four switchelements in each stage. A first stage 100 includes switch elements 141,142, 143 and 144, a second stage 102 includes switch elements 151, 152,153 and 154, and, a third stage 103 includes switch elements 161, 162,163 and 164. Each individual switch element is fabricated and operatesas was discussed for switch 70 (see also FIG. 3).

To illustrate how the apparatus of this invention functions to provideaccess through an interconnect device, such as MIN 10, from one of aplurality of input terminals or stations such as station 20 to any oneof a plurality of receiving terminals or stations such as station 33,assume that an operator at station 20 desires to send a data message tostation 33. First, station 20 sends the sacrificial routing packet tostage 100 via line 121 to MIN 10. This will result in switch element 141making a connection through line 122 to switch element 152 in stage 102.In the process of making this connection, the first sacrificial routingmessage within the packet is absorbed by first stage 100 of the MIN. Byallowing the absorption of this routing message, the switch elements(see also FIG. 3) are not required to buffer and forward messages forrouting purposes. The specific intermediate connections are determinedby the routing algorithm used (see also FIG. 3).

Once the first sacrificial routing message has established a connectionto stage 102, the sacrificial routing packet from station 20 containinga second stage 102 routing message travels via line 122 to switchelement 152, causing element 152 to make a connection through line 123to switch element 164. The third routing message within the sacrificialrouting packet from station 20 will then be present at third stage 103on line 123. This last stage 103 routing message will result in switchelement 164 making the final connection through line 125 to receivingstation 33. When this final connection has been made, the data packetportion of the transmission travels from the user at station 20 directlyto receiving station 33 along lines 121, 122, 123, and 125, which alsoconveyed the control information.

It should be noted that in the apparatus of this invention the number ofrouting messages (sometimes called switch configuration messages)required is equal to the number of stages in the multi-stageinterconnect network (MIN). Each of the routing messages causes aconnection through a single stage, and each routing message issacrificial, thus transmission of a routing message ends at the stage ofthe MIN where it actually operates on a switch element. Further, thereis no requirement for the queuing and retransmission of any routingmessage.

It should also be noted that though the above example of FIG. 6operation utilized three stages in MIN 10, the same operationalprinciples will apply to multi-stage interconnect networks having adifferent number of stages. For each stage of an MIN only one routingmessage or switch configuration message is required. Since each of theserouting messages is sacrificial and they are used only to configure apath through the MIN, these messages will never appear at the receivingstation.

FIG. 7 is a schematic diagram 170 showing the arrangement of datamessage 174 in relationship to routing messages 171, 172, and 173 forthe three stage switching system of MIN 10 (see also FIG. 6). Each ofrouting messages 171, 172, and 173 is a separate message containing aswitch position definition as its only data element.

For the example shown in FIG. 6, the entire four message packet ispresented to MIN 10 via line 121 (see also FIG. 6). Routing message 171causes switch element 141 to choose line 122 for routing to switchelement 152. Similarly, routing messages 172 and 173 cause switchelements 152 and 164 to select lines 123 and 125, respectively- As eachrouting message is sacrificed at the corresponding switch element, theresult is that data message 174 is output from MIN 10 via line 125.

FIG. 8 is a schematic diagram similar to that of FIG. 7 showing what isactually switched on the various lines of MIN 10 (see also FIG. 6). Theinput to MIN 10 via line 121 contains data message 174, along withrouting messages 171, 172, and 173. The output of MIN 10 via line 125 isonly data message 174, as shown.

Having thus described the preferred methods and embodiments of thepresent invention, those of skill in the art will readily appreciate theother useful embodiments within the scope of the claims hereto attached.

I claim:
 1. In optical data transfer apparatus, the improvementcomprising:a. a photonic interconnect network including a plurality ofswitch stages, each of said switch stages including a plurality ofswitches, each of said plurality of switches including a plurality ofinputs and a plurality of outputs; said outputs of each of saidplurality of switches in each of said plurality of switch stages areconnected to at least one of said inputs on each of said plurality ofswitches in the next succeeding stage of said plurality of switchstages; b. a sending terminal including a routing controller forselectively providing a plurality of sacrificial routing messages, andincluding a message source coupled to a first stage of said plurality ofswitch stages for providing a data message thereto, and furtherincluding a switch controller coupled to said plurality of switches forselectively connecting said sending terminal to one of said inputs onsaid plurality of switches in said first stage of said plurality ofswitch stages; and, c. a receiving terminal including a coupling meanscoupled to said receiving terminal and to said plurality of switches forconnecting said receiving terminal to a select one of said outputs on aselected one of said plurality of switches in the last stage of saidplurality of switch stages, for receiving said data message.
 2. Anapparatus according to claim 1 wherein the number of said plurality ofsacrificial routing messages is equal to the number of stages in saidplurality of switch stages.
 3. An apparatus according to claim 2 whereineach of said routing messages is sent to one selected switch of saidplurality of switches in each stage of said plurality of switch stages,and each of said routing messages is sacrificed at the selected one ofsaid switches.
 4. An apparatus according to claims 1, 2 or 3 whereinsaid switch comprises:a. a routing message decoder; b. a crossbarswitch; and, c. a switch controller connected between said decoder andsaid crossbar switch for toggling said switch in response to a decodedrouting message.
 5. An apparatus according to claim 4 wherein saidswitch further comprises a bi-directional crossbar switch.
 6. A methodof transferring data through a multi-stage interconnect network, whichnetwork includes a plurality of switches in each stage, comprising thesteps of:a. providing a plurality of switch configuration messages; b.sending a different message of said plurality of configuration messagesto only one selected switch in each plurality of switches in each stageof said network; c. sacrificing each of said switch configurationmessage after said switch configuration message has configured said oneselected switch; and, d. sending data through said multi-stageinterconnect network along the path created by said newly configuredswitches.
 7. A method according to claim 6 including the step ofproviding one of said switch configuration messages for each of saidstages.
 8. A method of establishing a transfer path through amulti-stage interconnect network which network includes a plurality ofstages, and each stage includes a plurality of switches, comprising thesteps of:a. providing a first sacrificial routing message to a firstselected switch of said plurality of switches in a first of saidplurality of stages; b. providing a second sacrificial routing messagethrough said first selected switch to a second selected switch of saidplurality of switches in a second of said plurality of stages; c.providing a third sacrificial routing message through said first andsaid second selected switches to a third selected switch of saidplurality of switches in a third of said plurality of stages; and, d.providing further sacrificial routing messages as needed to select afinal switch of said plurality of switches in a final stage of saidplurality of stages, each of said further routing messages passingthrough all previously selected switches to a further selected switch ofthe plurality of switches in a next succeeding stage of said pluralityof stages.
 9. In a system for the transfer of data messages through amulti-stage interconnect network having L through n stages and aplurality of switches in each stage, the apparatus comprising:a. amessage origination station for sending a data message through saidinterconnect network and for sending a plurality of sacrificial routingmessages to determine a path through said network for said data message;b. first routing means for routing a first of said routing messages to afirst selected switch of said plurality of switches in a first of saidstages; c. second routing means for routing a second of said routingmessages through said first selected switch to a second selected switchof said plurality of switches in a second of said stages; and, d. a pathfor connecting an nth of said routing messages through n+1 of saidselected switches to an nth selected switch of said plurality ofswitches in the nth of said stages.